Preparation Of Sodium Pyrophosphate-modified Sludge Biochar And Its Adsorption For Cu(Ⅱ) From Wastewater

In recent years,with the rapid advancement of urbanization process,the output of municipal sludge will increase continuously in China.The potential environmental risks caused by municipal sludge will increase if it is not treated effectively.In order to realize effective treatment and resource utilization of sludge,sodium pyrophosphate-modified sludge biochar(SP-SBC)was prepared by an impregnation method and used to adsorb Cu(Ⅱ)from wastewater in this study.Firstly,the optimal modification conditions for the preparation of SP-SBC were selected.Secondly,the physicochemical properties of SP-SBC that prepared under the optimal conditions and original sludge biochar(SBC)were determined and analyzed.And then,the static adsorption experiments were carried out to investigate the Cu(Ⅱ)adsorption behaviors and mechanisms of SP-SBC.Finally,the dynamic adsorption characteristic of SP-SBC for Cu(Ⅱ)was also explored.The main conclusions are as follows:The optimal modification conditions for the preparation of SP-SBC were concentration of sodium pyrophosphate 60 g/L,modification time 12 h,solid-liquid ratio 1:20,and modification temperature 25 ℃.Compared with these of SBC,the yield,ash content,pH value,Na and P contents of SP-SBC were higher,while K,Ca,and Mg contents were lower;SEM results showed that the surface of SP-SBC was rougher;through FT-IR analysis,it was found that surface functional group types of SP-SBC did not change,but the intensity of each peak all decreased;XRD analysis demonstrated that pyrophosphate was introduced into SP-SBC.In the comparison experiment,the Cu(Ⅱ)adsorption capacity of SP-SBC at equilibrium time was 4.55 times than that of SBC,indicating that modification of sodium pyrophosphate was beneficial to Cu(Ⅱ)adsorption.Although SP-SBC contained a certain amount of heavy metals(Fe,Zn,Mn,Pb,Cu,Cr,Ni,Co,Cd,and etc.),the leaching concentrations of these heavy metals were all lower than the limits of China national standards.The results showed that SP-SBC was a safe adsorption material.In the static adsorption experiment of SP-SBC for Cu(Ⅱ),SP-SBC dosage,initial pH value,adsorption time,adsorption temperature,and ionic strength can affect the adsorption of Cu(Ⅱ)on SP-SBC.The appropriate SP-SBC dosage and initial pH value was 2 g/L and5.0,respectively,and the equilibrium time was 12 h.The Cu(Ⅱ)adsorption capacity increased with the increase of adsorption temperature,while it decreased as the ionic strength enhanced.The Cu(Ⅱ)adsorption process on SP-SBC was well described by the pseudo-second order model,which reflected that the rate-limiting step of the adsorption was chemical adsorption.The adsorption thermodynamic data were perfectly fitted by Freundlich model,which indicated that the Cu(Ⅱ)adsorption process was multi-molecular layer adsorption.△G° was negative,and△H°,△S° were positive,which showed that the adsorption of Cu(Ⅱ)on SP-SBC was spontaneous and endothermic.FT-IR analysis of SP-SBC before and after adsorption demonstrated that oxygen-containing functional groups had a negligible effect on the adsorption of Cu(Ⅱ).The Cu(Ⅱ)adsorption mechanism of SP-SBC included ion exchange,electrostatic attraction,and precipitation.In the dynamic adsorption experiment,the Cu(Ⅱ)adsorption process of SP-SBC was affected by bed height,flow rate,Cu(Ⅱ)concentration,and initial pH value.Increasing bed height and initial pH value was beneficial to prolong breakthrough time and saturation time,while they shorted with the increase of flow rate and Cu(Ⅱ)concentration.Both Thomas model and BDST model could well fit the dynamic adsorption process of Cu(Ⅱ)on SP-SBC.The fitting parameters of the two models can provide parameters of adsorption rate and maximum adsorption capacity for the industrial application of SP-SBC in the treatment of Cu(Ⅱ)wastewater.Taking NaOH as desorption agent,after three cycles of desorption,the equilibrium adsorption capacity was 32.76%of the initial adsorption capacity,indicating that NaOH could be used for the desorption and regeneration of adsorption column.Overall,SP-SBC can be used for the adsorption of Cu(Ⅱ)from wastewater.The research provides an efficient and new way for resource utilization of sludge in heavy metal pollution control of water body.